The invention relates to wireless communications networks.
Wireless communications networks include base stations linked to mobiles. Upon request from a mobile, a base station is able to establish communication with that mobile. This communication facilitates an exchange of speech or digital data between users.
Such communication can be effected by means of a “downlink”, in which case the communication is established from the base station to the mobile. The expression “downlink” or “down channel” refers to the case where the base station seeks to establish or maintain communication to the mobile.
In a wireless communications network, the base stations provide services to the mobiles. A mobile requests a certain service which is composed of data to be transmitted under certain conditions (for example data rate or timing). An “active” mobile is a mobile that is receiving such a service.
The mobile may request two types of services, namely real time services with predefined data rates and deferred services with flexible data rates.
Normal operation of a wireless communications network relies on load control. Load control facilitates the management of access (also termed “admission control”) of a mobile to a given base station, together with management of the load of a given base station (also termed “congestion control”) to ensure quality of service (QoS). More precisely, admission control serves to determine for a given base station whether a new mobile can be served by the base station, while congestion control serves to control the load induced by all of the mobiles served by the base station (referred to as “active” mobiles).
The document “Downlink admission control strategies for cdma systems in a manhattan environment. Vehicular Technology Conference, 2:1453-1457, 1998” by M. Persson, J. Knutsson, P. Butovitsch and R. D. Yates, describes so-called “direct load control” schemes.
In “direct load control” schemes, load control is based on a comparison between a load indicator computed for a given base station and a threshold value referred to as the load threshold. In these configurations, admission control allows access by a new mobile to a given base station if it can be served without pushing the load indicator beyond the load threshold. In downlink communications networks, such a load indicator generally depends on the transmission power of the base station which fluctuates over time. The load threshold must therefore be specified with a large safety margin. Moreover, the additional load induced by a new mobile is estimated in an approximate manner. Also, in such direct load control schemes, communication outages can occur, even instantaneously following the admission of a new mobile and access to a base station may be denied to more mobiles than necessary.
The document “Soft and safe admission control in cellular networks. IEEE Transaction on Networking, 5(2):414-418, April 1997” by Zvi Rosberg, Michael Andersin and Jens Zander, and the document “Channel access algorithms with active link protection for wireless communication networks with power control, IEEE/ACM Transactions in Networking, 8(5):583-596, October 2000” by N. Bambos, S. C. Chen and G. J. Pottie, describe other arrangements referred to as “test load control” schemes.
In “test load control” schemes, admission control temporarily allows a new user access to a base station until a decision is taken. Test load controls have the advantage of ensuring that no cutoff will occur, at least at the time when the decision is taken, but have the drawback of being excessively long, so that they are rarely usable in practice.
French patent application No. 03 02 017 proposes a load control process and scheme based on a comparison between a load indicator computed for a given base station, and a threshold value, termed the load threshold, as in direct load control schemes.
In patent application No. 03 02 017, the load indicator depends only on the attenuations between the users and the antennas, and on the signal-to-interference-and-noise ratios (SINR). Thus, they do not depend on the transmission powers. However, in the process and scheme described in this patent application, load control is exercised without taking power limitations into account. Such power limitations are generally imposed by a standard which fixes the maximum power that a base station is allowed to emit.